Abstract

Thin films that have high transparency and conductivity are used in various applications such as displays, solar cells, electrochromic devices and heatable glasses (Granqvist and Hultåker, 2002;1-5). This present work describes the deposition of transparent and conductive In2O3 films using a pulsed d.c magnetron sputtering technique from In2O3 powdered targets. The films deposited at various oxygen concentrations were approximately 500 nm in thickness, were pin hole free and well adhered to cleaned glass substrates. Films were analyzed using x-ray diffraction, four point probe, hot probe, uv-vis spectroscopy, AFM and Dektak profilometer. The structural and electrical analyses revealed that the films were crystalline and highly conductive when prepared in the absence of oxygen during sputtering. A dramatic change in resistivity was observed when oxygen was introduced during deposition. Resistivity increased from 0.004 cm (no oxygen) to 10 cm with 10% oxygen. However the corresponding transmissivity improved from 85% to 95% when the oxygen content was increased. The main focus of our research is to find an alternative buffer layer for CuInSe2 based solar cells. A typical CIS cell is in the form of a heterojunction of ZnO/i-ZnO/CdS/CuInSe2/ Mo/Glass substrate. The n-type CdS layer is the buffer layer (Cui and Xi, 1996;325-9) and the intrinsic ZnO layer is a high resistance layer to minimize the leakage current (Ishizuka et al., 2005;541-8). From our studies it is clear that a highly conducting n-type In2O3 layer can be made by sputtering without oxygen and a high resistive In2O3 layer can be deposited with 10% oxygen. This could potentially replace the i-ZnO/CdS junction. We can form an n-type highly conducting layer or a highly resistive layer simply by adjusting the oxygen flow during In2O3 deposition. This could cut down the cost of an extra deposition process and lead to a cadmium-free solar cell.